1. Technical Field of the Invention
The present invention relates to a battery pack having a structure that prevents reliability degradation, a breakdown or malfunction caused by unauthorized disassembling or modification of the battery or parts of the battery pack.
2. Description of the Related Art
When the rechargeable battery of a battery pack that is used as the power source of equipment has come to the end of its life after repeated charge and discharge, the whole battery pack is supposed to be replaced, but sometimes the user may replace only the rechargeable battery by himself. Also, there is a dealer who provides service of changing rechargeable batteries of battery packs so that the packs can be used again.
However, battery packs usually include a control circuit suitably designed for the characteristics and performance of the rechargeable batteries and for a loading device and a charging device to which the battery pack is connected. The rechargeable battery in the pack should always be replaced by the same type of battery made by the same manufacturer and having the same characteristics and performance, which is hard to achieve because there are variations in the characteristics and performance even among the batteries made by the same manufacturer. Not to mention, if the battery is replaced with a product of a different manufacturer, or a wrong type of battery, the battery pack reliability is lost, and the equipment that uses such a modified battery pack may malfunction, break down, or cause an accident.
Moreover, most battery packs are made up of a combination of two or more rechargeable batteries having corresponding characteristics and performance, with a control circuit designed in accordance with the types of rechargeable batteries to secure desired performance and reliability. Therefore, batteries that meet the same standards may not necessarily promise designed performance, and moreover, the battery pack protection mechanism for preventing abnormal heat generation or volume expansion of batteries may not function normally.
It is important to prevent battery packs from being disassembled and modified by a person or a dealer other than the manufacturer or a dealer designated by the manufacturer for securing reliability and credibility of the manufacturer to the users. Accordingly, there are known a battery pack structure that prevents disassembling or modification, and an adhesive tape that leaves a mark when the battery or other parts are removed for preventing modification (see Japanese Patent Publication No. 2003-084672).
The battery pack needs to be compatible with the loading device which operates by the battery discharge power and with the charging device which supplies power to the batteries, and requires a feature for preventing an unauthorized product to be connected and preventing the battery pack from being charged in a wrong manner, so as to prevent damage to the loading device or to the rechargeable batteries. Counterfeit battery packs, in particular, which appear exactly the same as the genuine battery pack, are widespread, and many accidents have been reported, including a fire accident of a counterfeit battery pack and damage to the equipment for which a counterfeit was used. Therefore, there have been demands for development of means for distinguishing a counterfeit from a genuine product and means for preventing a wrong battery pack to be connected to a loading device and a charging device, and as one example to meet these demands, a battery pack structure is known in which an IC tag outputs a true or false signal in response to a corresponding radio wave signal from the loading device and charging device (see Japanese Patent Publication No. 2003-168406).
A battery pack is not just a rechargeable battery encased in a pack case but includes a circuit substrate, on which are formed a protection circuit for protecting the rechargeable battery from overcharging or overdischarging, a circuit for calculating remaining power, and a power source control circuit for controlling the operating state of the battery. If the rechargeable battery or circuit substrate is improperly modified or changed, the battery pack cannot be guaranteed to operate correctly, and moreover, it may lead to abnormal heat generation or volume expansion of the battery. The same applies with a counterfeit battery pack, since its rechargeable battery and circuit substrate are not correctly configured.
There is a limit, however, to prevent modification by structural measures, and a trace of modification is sometimes deftly concealed. The problem was that, because of this difficulty in preventing modification in a reliable manner, it is always after a breakdown or accident has occurred that the battery pack is found to have been modified.
The conventional IC tag is effective in recognizing a counterfeit, but was useless in detecting an act of modification.